The present invention relates to a susceptor that thermally heats a food product such as a garnished flat raw dough disposed thereon when exposed to a microwave energy field and which improves the cooking, browning, and crisping of food products made of bread in a more natural manner close to the heating effect that is produced in conventional ovens.
Microwave ovens often provide a quick and convenient way of cooking and heating food substances. A microwave oven typically heats food substances more quickly than a conventional oven even those using forced convection. The microwave energy heats the food product differently, however, from a conventional oven. In a conventional oven, the high temperature atmosphere impinges on the surface of the food product, causing the surface to heat first. Moisture is driven from the exterior of the food product by the hot oven atmosphere which results in both a progressive moisture evaporation at the surface of the product, and consequently, in a proper and homogeneous browning and crisping of the full product. The heat transfer takes place from the periphery to the center of the product by slow heat transfer mechanisms, especially conduction. As a result, the product can be made fully cooked in the middle and browned on the surface.
Heating in a microwave oven involves different phenomena. A microwave oven generates high intensity, high frequency electromagnetic radiation that penetrates into the food product. Heating occurs when the food product absorbs the electromagnetic energy. The wave absorption at the surface of the product is insufficient to provoke a superficial browning of the product. In addition, during the microwave heating, the moisture is also transferred from the interior to the exterior of the product due to the evaporation of the free water contained therein. In particular with dough-based products, the heating effects of microwave energy penetrate to a much greater depth toward the center of the food product than in the case of conventional heating. As a result, the middle of the food product will be heated much more quickly, while the surface will not be heated sufficiently to generate non-enzymatic browning reactions and to achieve desirable crispness. The problem of heating in microwave ovens is exacerbated in the particular case of frozen food products, such as frozen uncooked pizzas and the like. Frozen products comprise an amount of frozen water molecules and frozen fat molecules that is less sensitive to the microwave energy than the non-frozen part of the molecular system. As a result, the product has a tendency to heat in a non-homogeneous manner and zones of the product may frequently still be frozen while other parts are fully cooked.
In an attempt to overcome the drawbacks of microwave heating, susceptors have been developed which are usually added to the packaging of the food product. In the particular domain of garnished flat dough products such as pizzas, plate-like susceptors are known that are generally disposed underneath as a support for the dough which converts microwave energy into thermal energy. The thermal energy produces browning and crisping of the food item situated directly in contact with it. A typical susceptor includes a thin layer of microwave-interactive plastic such as aluminum deposited on a foodgrade plastic surface. Typically, a sheet of thick paper or cardboard further reinforces the susceptor bonded underneath, incidentally to confer sufficient rigidity to hold the food product.
U.S. Pat. No. 4,896,009 to Pawlowski (xe2x80x9cPawlowskixe2x80x9d) provides a susceptor for food items wherein the base laminate contains gas permeable means, such as holes, that are located in the immediate area of the center of the base laminate. Holes with an average diameter of xe2x85x9c inch are produced to allow venting of gases and vapors to improve browning and crisping of the crust.
Several drawbacks remain, however, when heating an uncooked flat dough-type product such as a pizza or pizza-like product in a microwave oven. A pizza crust as obtained from a susceptor such as the one described in Pawlowski also looks undesirably burned underneath the rim of the dough, while the center of the dough looks relatively uncooked because of the presence of relatively large holes in there. It is believed that, although venting in the middle is well provided, the presence of large holes in the middle causes this region of the crust to heat less rapidly than at the edges that come more quickly to a sufficient degree of cooking. Therefore, the crust as obtained does not fit the normal standard of conventional pizza-type products that is required to gain widespread consumer acceptance.
A similar approach is described in European Patent Application No. 0943558 which describes an imperforate susceptor in which transparent microwave zones are provided in the central region of the susceptor. This approach differs from that in Pawlowski in that the transparent areas are preferably not gas permeable means, but rather are inactivated metallized areas or non-metallized areas of the susceptor. This solution is not well adapted to bake frozen raw dough as it does not solve the cracker-like texture of the rim, but even makes the heating still more unsatisfactory since, contrary to Pawlowski, the venting of the center part of the pizza is no longer obtained. If the water vapor cannot evacuate under the pizza, the crust becomes soggy and moist at the bottom. This undesirable phenomenon is further enhanced as the center has a plurality of areas that are non-reactive to the microwave field, which forms white crust areas with a soggy and soft texture.
U.S. Pat. No. 5,278,378 to Beckett describes a microwave heating element with circular openings therethrough and antenna means in at least some of the openings to guide microwave energy to and through the openings. The openings are provided uniformly along the entire surface of the heating element to affect a uniform heating of the product. The openings serve to guide portions of the microwave energy therethrough, and are, therefore designed specifically with inner structures such as small islands, peninsulas or continuous strips. This design is for uniform heating of a homogeneous foodstuff, but does not properly take into account the specificity of a garnished flat bread product, which is a difficult product to heat. Furthermore, it is well known that such structures may create undesirable sparks.
The invention relates to a microwave susceptor for heating food products such as garnished flat doughs in a microwave oven. This susceptor is advantageously in the form of a metallized plate having a plurality of apertures forming gas and microwave energy permeable areas, which apertures are disposed in an area disposed about a peripheral portion of the plate, with each aperture having a transverse dimension of at least about 5 mm.
In one embodiment, the plurality of apertures are confined on the metallized plate within a peripheral band having a predetermined width, whereas the rest of the plate is free from such apertures. The peripheral band preferably has a width of between about 5 mm to less than about 50 mm and the apertures are located between about 5 mm and about 20 mm from the nearest edge of the plate. In a preferred embodiment, the plate is disc shaped and has a diameter of about 200 mm to 230 mm.
In another embodiment, the plate includes a central area externally delimited by the peripheral band, the central area having a plurality of perforations each having a maximum transverse dimension of less than about 1.5 mm. Preferably, the perforations include slits having a length of at least about 10 mm.
In another embodiment, the plurality of apertures include regular polygonal shapes, or irregular polygonal shapes, or any combinations thereof. In a preferred embodiment, the plurality of apertures includes circular shapes, oval shapes, or both circular and oval shapes.
In yet another embodiment, the apertures have a length of between about 5 mm to about 15 mm and are distributed so as to have a distance of about 10 to 38 mm between each aperture. In still another embodiment, the plate includes a laminate including a receiving surface onto which the garnished flat dough can be pressed, the receiving surface comprising a food-grade, metallized plastic layer, and a rigid microwave-inert substrate that forms the lower surface of the plate adhesively attached to the receiving surface. Preferably, the microwave-inert substrate is a flat or corrugated material and is attached to the receiving surface by an adhesive. In a preferred embodiment, the corrugated material has a thickness of about 1 mm to 1.5 mm before it is corrugated.
The invention further relates to an article including a susceptor plate having a metallized plastic surface, and an uncooked food product located on the metallized plastic surface. Preferably, the food product is an uncooked dough, such as a garnished flat dough product comprising a substantially non-garnished dough rim and a garnished center. A plurality of apertures having transverse dimensions of at least about 5 mm are distributed within the susceptor plate within a peripheral band having a predetermined width, whereas the rest of the plate is free from such apertures, and wherein the flat dough product is disposed onto the plate so that the peripheral band substantially encompasses the limits of the non-garnished dough rim of the flat dough product.
In a preferred embodiment, the apertures each have a transverse dimension of about 5 mm to 15 mm and a length of up to 15 mm, the apertures being distributed so as to have a distance of about 10 mm to 38 mm between each aperture. In another embodiment, the width of the band is about 35 mm to 50 mm. In a preferred embodiment, the apertures cover about 8% to 15% of the surface area of the band, the apertures having surface areas of about 30 mm2 to 40 mm2 each. In another embodiment, the flat dough product is frozen and the flat dough product may be a pizza.